North Korea has been struck by an “explosion” of 6.3 magnitude, according to the US Geological Service (USGS).
The tremor was recorded at a depth of six miles (10 kilometres) on the east coast of North Korea.
USGS initially recorded the tremor at a magnitude of 5.2, but it was later revised amid World War 3 fears.
China’s earthquake administration said it detected a 6.3 magnitude earthquake in Northeastern North Korea, calling it a “suspected explosion,” it has been reported.
Recent tremors in North Korea have been caused by nuclear tests, experts have said.
There are no immediate reports of damage or casualties.
South Korea’s government has said that the North may have conducted another nuclear test.
South Korean officials have claimed the quake took place in Kilju County, where the North’s Punggye-ri nuclear test site is situated.
President Moon Jae-in of South Korea called an emergency meeting of his National Security Council in response to the report.
The news comes after North Korea announced it has developed a more advanced nuclear weapon that has “great destructive power”.
Kim Jong-un’s state media mouthpiece NCNA declared the hydrogen bomb’s power is adjustable to hundreds of kilotons and can be detonated at high altitudes.
It also boasted that these latest components would allow the country to build as many nuclear weapons as it wants.
KCNA reported: “Kim Jong-un said he felt the pride at the indomitably bolstering up of [North Korea’s] nuclear forces despite a great price as he watched the Juche-oriented thermonuclear weapon with super explosive power made by our own efforts and technology.
“He expressed great satisfaction over the fact that our scientists can do anything without fail if the party is determined to do.
“The scientists further upgraded its technical performance at a higher ultra-modern level on the basis of precious successes made in the first H-bomb test.”
KCNA also hit out at earlier reports that its missile parts were imported from the Ukraine as it declared its hyrdrogen bomb was entirely homemade.
It said: “All components of the H-bomb were homemade and all the processes ranging from the production of weapons-grade nuclear materials to precision processing of components.”
Japanese Prime Minister Shinzo Abe also spoke with US President Donald Trump by phone on Saturday evening (Sunday local time) and said that in the face of an “escalating” situation close cooperation between their countries and South Korea was needed.